In the fabrication of electrical circuits, it is often desirable to couple a circuit component to a substrate. For instance, one particular example involves the coupling of an integrated circuit chip to a ceramic substrate or to a printed circuit board. Although various techniques exist, adhesives are widely used to couple circuit components to substrates.
Conventional fabrication techniques apply adhesive to the substrate. The circuit components are then placed onto the adhesive on the substrate. One popular and very efficient method for applying adhesive onto a substrate is referred to as a screen printing process. In a screen printing process, a screen that is generally impermeable to adhesive has adhesive placed on it. The screen includes a pattern of holes formed in it, and these holes correspond to desired locations of circuit components on the substrate. When the screen pattern is placed over the substrate, a squeegee moves along the screen and over the holes, so that the adhesive passes through the holes and onto the underlying substrate.
The screen printing process works quite well on substrates that are substantially flat, and it provides a relatively flat adhesive patch that corresponds to the shape of the circuit component to be placed on the substrate. However, the screen printing process does not work well on multi-level substrates or on substrates that include ridges or cavities. On substrates with such surface irregularities, it is difficult for the screen to remain in contact with the substrate as the squeegee passes over the screen. As a result, the adhesive may not be properly transferred from the screen to the substrate.
To deposit adhesive on non-flat substrates, dispensing machines are typically used. Dispensing machines use a plurality of needles to dispense drops of adhesive onto a substrate at the desired locations. Although dispensing machines are able to deposit adhesive on non-flat substrates, such machines unfortunately exhibit various other disadvantages. First, dispensing machines deposit drops of adhesive, rather than carefully formed and relatively flat adhesive patterns such as those produced by screen printing. When circuit components are placed on these drops, the adhesive may not distribute evenly between the component and the substrate. Second, dispensing machines are relatively slow compared to screen printing machines. As is well known, slower techniques tend to limit throughput and increase manufacturing costs. Third, certain very desirable adhesives cannot be dispensed by dispensing machines due to their physical and/or chemical properties.
The present invention may address one or more of the problems discussed above. The invention further develops the invention of Ulmer and Pham, "Method and Apparatus for Use in Assembling Electronic Devices", U.S. application Ser. No. 09/154,810, which is also assigned to the assignee of this invention. This disclosure of that application is incorporated herein by reference.